1. Field of the Invention
The present invention relates to a semiconductor laser device which uses a semiconductor laser having a plurality of light-emitting portions, and independently detects a plurality of beams, a light amount control device for controlling the light amount of the semiconductor laser, and an image forming apparatus such as a laser printer, or the like.
2. Related Background Art
As an apparatus for controlling the light amount using a semiconductor laser having a plurality of light-emitting portions, for example, a laser printer disclosed in Japanese Laid-Open Patent Application No. 57-23289 is known. In this laser printer, a plurality of beams emitted by the semiconductor laser are scanned and irradiated onto the surface of a photosensitive drum to form an image by electrophotography.
In this case, as described in, e.g., Japanese Laid-Open Patent Application No. 9-164722, the light amount control is attained by detecting light outputs from a plurality of light-emitting portions of the semiconductor laser using a single photodetector.
However, especially in case of a semiconductor laser which comprises a plurality of light-emitting portions on a monolithic semiconductor laser chip, when a current is supplied to one light-emitting portion, heat produced by that portion is conducted to other light-emitting portions, and lowers the emission efficiency of these light-emitting portions, resulting in an emission amount drop (such phenomenon is called thermal interference).
When the emission amount drops, density nonuniformity occurs in an image upon writing the image by the laser beam printer, thus deteriorating the image quality.
It is, therefore, an object of the present invention to provide a semiconductor laser device which can remove variations of front beam output light amounts due to thermal interference among a plurality of light-emitting portions and can obtain a high-quality image by independently detecting a plurality of beams output from the light-emitting portions, and controlling the light amounts in real time in units of light-emitting portions, a light amount control device for controlling the light amount of a semiconductor laser, and an image forming apparatus such as a laser printer, or the like.
A semiconductor laser device of the present invention comprises a semiconductor laser chip formed with a first light-emitting surface which is formed on one end face of the chip and outputs a plurality of front beams, and a second light-emitting surface which is formed on an end face opposite to the first light-emitting surface of the semiconductor laser chip and outputs a plurality of back beams corresponding to the plurality of front beams, and back beam detection means formed to face the second light-emitting surface of a light-emitting portion of the semiconductor laser chip and having a plurality of photodetection portions for independently detecting the plurality of back beams output from the second light-emitting surface, the back beam detection means being in tight contact with the second light-emitting surface of the semiconductor laser chip.
The back beam detection means may be adhered to the semiconductor laser chip by an adhesive.
The plurality of photodetection portions of the back beam detection means may be formed on a single substrate to be isolated from each other.
The back beam detection means may be attached to the second light-emitting surface of the semiconductor laser chip with a local region thereof extending therefrom, and a lead electrode may be formed on the local region that extends upon attachment.
A semiconductor laser device of the present invention comprises a semiconductor laser chip formed with a first light-emitting surface which is formed on one end face of the chip and outputs a plurality of front beams, and a second light-emitting surface which is formed on an end face opposite to the first light-emitting surface of the semiconductor laser chip and outputs a plurality of back beams corresponding to the plurality of front beams, and back beam detection means obliquely formed on the second light-emitting surface of a light-emitting portion of the semiconductor laser chip and having a plurality of photodetection portions for independently detecting the plurality of back beams output from the second light-emitting surface.
The back beam detection means may be set on an inclined surface of a light transmission member.
Light-shielding means may be inserted between light beams that enter the photodetection portions of the back beam detection means.
A mirror may be inserted between light beams that enter the photodetection portions of the back beam detection means.
An optical filter may be interposed between the second light-emitting surface of the semiconductor laser chip and the back beam detection means.
A semiconductor laser device of the present invention comprises a semiconductor laser chip formed with a first light-emitting surface which is formed on one end face of the chip and outputs a plurality of front beams, and a second light-emitting surface which is formed on an end face opposite to the first light-emitting surface of the semiconductor laser chip and outputs a plurality of back beams corresponding to the plurality of front beams, a transparent insulating layer which is formed on the second light-emitting surface and transmits light therethrough, and back beam detection means formed on the transparent insulating layer and having a plurality of photodetection portions for independently detecting the plurality of back beams output from the second light-emitting surface.
The plurality of photodetection portions of the back beam detection means may include an n-type semiconductor layer formed on the transparent insulating layer, and a p-type semiconductor formed on the n-type semiconductor layer.
A lead electrode may be formed on a surface of the n- and p-type semiconductor layers.
The back beam detection means may be formed by epitaxial growth or deposition.
Also, a light amount control device of the present invention comprises a semiconductor laser device having the above-mentioned back beam detection means, and light amount feedback control means for independently controlling the amounts of front beams output from the first light-emitting surfaces on the basis of the amounts of light detected by photodetection portions of the back beam detection means in the semiconductor laser device.
Furthermore, according to the present invention, an electrophotographic image forming apparatus which forms an image by irradiating laser beams emitted by the aforementioned semiconductor laser device onto the surface of a photosensitive body, comprises the above-mentioned light amount control device, and can form the image using laser beams, the amounts of which are controlled by the light amount control device.